1. Field
The embodiments relate to a robot walking control apparatus and a method thereof, and more particularly, to a robot walking control apparatus, which removes an ineffective motion in a torque-based walking robot, and a method thereof.
2. Description of the Related Art
Recently, biped walking robots, which have a joint system similar to that of a human being, and easily walk with two feet in human working and living spaces, have been vigorously researched and developed. Bipedal walking has disadvantages, such as instability and difficulty in pose control or walking control, as compared with quadruped walking or hexapod walking. However, bipedal walking has advantages, such as more flexibly coping with a discontinuous walking surface, i.e., an uneven surface of the ground, or stairs.
Methods of controlling the bipedal walking of a robot include a position-based (meaning the following of a target position of a robot joint), zero moment point (hereinafter, referred to as ‘ZMP’) control method, and a torque-based (meaning the following of a target torque of a robot joint) finite state machine (hereinafter, referred to as ‘FSM’) control method.
In the ZMP control method, a walking direction, a step width, and a walking speed are set in advance so that a ZMP of a robot satisfies a ZMP constraint, i.e., a condition that the ZMP is located in a safety area within a support polygon composed of a supporting leg or supporting legs. When the robot is supported by one foot, the safety area is the area of this foot. When the robot is supported by both feet, the safety area is the area having a small size within a convex polygon including areas of both feet. Walking patterns of respective legs corresponding to the set items are generated, and walking trajectories of the respective legs are calculated according to the walking patterns. Further, positions of joints of the respective legs are calculated through an inverse kinematical equation of the calculated walking trajectories, and target control values of the respective joints are calculated based on current positions and target positions of the respective joints. Further, a servo control, in which the respective legs follow the calculated walking trajectories per control time, is carried out. When the respective legs are deviated from the walking trajectories in walking, torques of motors are controlled so that the respective legs exactly follow the walking trajectories.
In the FSM control method, a robot does not walk by following positions per control time, but properly walks by referring to motion states of the robot, which are defined in advance, in walking. That is, in the FSM control method, states of the respective motions of a walking robot (meaning states in an FSM) are defined in advance, target torques of respective joints are calculated with reference to the states of the respective motions in walking, and the joints are controlled such that the joints follow the target torques, thereby allowing the robot to properly walk.
The torque-based FSM control method is a control method, which is generally based on torque instructions, is applied to the structure of an elastic mechanism using back-drivability and thus has high energy efficiency, and has low rigidity and thus is generally safe. The torque-based FSM control method allows the robot to assume various poses by converting the motion state of the robot in walking, but causes the robot to perform a separate motion to maintain its balance regardless of the walking motion to accomplish a given task due to the selection within the restricted motion states. A step motion of stamping the foot of the robot is typical of this balancing motion. Such a motion may be unnecessary if the robot maintains its balance, and thus causes time delay and energy waste due to inefficiency.